US-20260126511-A1 - Direction Finding Using a Single Electrically-Small Electromagnetic Field Sensing Device

US20260126511A1US 20260126511 A1US20260126511 A1US 20260126511A1US-20260126511-A1

Abstract

A system for direction finding comprising: a single electrically-small radio frequency (ESRF) device configured to measure an amplitude of an incoming RF signal; a docking stage configured to rotate about a center axis, wherein the ESRF device is mounted to the docking stage such that with each rotation of the docking stage, the ESRF device passes through a plurality of discrete rotational positions so as to replicate a circular array of ESRF devices; and a processor configured to calculate an angle of arrival (AoA) of the incoming signal based on the measured amplitude of the incoming RF signal at each of the plurality of rotational positions.

Inventors

Sergio A. Montoya
Benjamin J. Taylor

Assignees

THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY

Dates

Publication Date: 20260507
Application Date: 20241107

Claims (20)

1 . A system for direction finding comprising: a single electrically-small radio frequency (ESRF) device configured to measure an amplitude of an incoming RF signal; a docking stage configured to rotate about a center axis, wherein the ESRF device is mounted to the docking stage such that with each rotation of the docking stage, the ESRF device passes through a plurality of discrete rotational positions so as to replicate a circular array of ESRF devices; and a processor configured to calculate an angle of arrival (AoA) of the incoming signal based on the measured amplitude of the incoming RF signal at each of the plurality of rotational positions.
2 . The system for direction finding of claim 1 , wherein the ESRF device is mounted to the docking stage at an oblique angle to the center axis.
3 . The system for direction finding of claim 2 , wherein the docking stage is mounted to a stationary platform.
4 . The system for direction finding of claim 1 , further comprising an active field source configured to generate a magnetic field to compensate for the ESRF’s motion through a surrounding magnetic background.
5 . The system for direction finding of claim 4 , wherein the surrounding magnetic background is Earth’s magnetic field.
6 . The system for direction finding of claim 5 , wherein the system is fixed within a cryogenic environment.
7 . The system for direction finding of claim 5 , wherein the ESRF is tuned to receive the incoming RF signal from a particular RF source of interest.
8 . The system for direction finding of claim 7 , wherein ESRF is tuned to be sensitive to a magnetic field component of the incoming RF signal.
9 . The system for direction finding of claim 1 , wherein the incoming RF signal is circularly polarized and the processor is configured to use an interferometry-based model to calculate the AoA.
10 . A method for direction finding using a single electrically-small radio frequency (ESRF) device comprising: mounting the ESRF device to a docking stage that is configured to rotate about a z-axis, rotating the docking stage about the z-axis at a rotational speed optimized to facilitate detection of RF signals within a desired frequency bandwidth; monitoring an amplitude of an incoming signal at N rotational positions during each revolution of the docking stage so as to generate at least N samples thereby replicating a circular array of ESRF devices; and calculating an angle of arrival (AoA) of the incoming signal based on the at least N samples.
11 . The method for direction finding of claim 10 , wherein the incoming RF signal is a linearly polarized RF signal.
12 . The method for direction finding of claim 11 , wherein the docking stage is mounted to a stationary platform.
13 . The method for direction finding of claim 12 , further comprising a magnetic field generating element with an active field source to compensate for the ESRF’s motion through a surrounding magnetic background so as to keep a magnetic field at a surface of the ESRF at a constant value.
14 . The method for direction finding of claim 13 , wherein the surrounding magnetic background is Earth’s magnetic field.
15 . The method for direction finding of claim 14 , further comprising mounting the docking stage within a cryogenic environment.
16 . The method for direction finding of claim 15 , wherein the ESRF is tuned to receive the incoming RF signal from a particular RF source of interest.
17 . The method for direction finding of claim 10 , wherein the incoming RF signal is circularly polarized and further comprising using an interferometry-based model with the processor to calculate the AoA.
18 . The method for direction finding of claim 10 , wherein N is equal to three.
19 . The method for direction finding of claim 10 , wherein N is equal to 360 .
20 . The method for direction finding of claim 10 , wherein the monitoring step comprises generating at least 2 N samples such that two amplitude measurements are collected at each rotational location, and the AoA is calculated based on the 2 N samples.

Description

FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT The United States Government has ownership rights in the invention claimed herein. Licensing and technical inquiries may be directed to the Office of Research and Technical Applications, Naval Information Warfare Center Pacific, Code 72110, San Diego, CA, 92152; voice (619) 553-5118; NIWC_Pacific_T2@us.navy.mil. Reference Navy Case Number 108774. BACKGROUND OF THE INVENTION Common methods to determine the angle of arrival (AoA) of a radio frequency (RF) signal employ the use of at least two RF devices that are separated by a distanced commonly referred as the baseline. Interferometry-based AoA systems commonly look at phase differences of an RF signal received on at least two RF devices at different moments in time. Since the phase difference can only be made with respect to 2π, there is an inherent ambiguity in the calculated AoA along certain axes. To resolve this, more RF devices are frequently used, which may be arranged in various dimensions, to increase the angle fidelity at the expense of increased computational operations. There is a need for an improved direction finding device. SUMMARY Described herein is an embodiment of a system for direction finding comprising an electrically-small radio frequency (ESRF) device, a docking stage, and a processor. The ESRF device is configured to measure an amplitude of an incoming RF signal. The docking stage is configured to rotate about a center axis. The ESRF device is mounted to the docking stage such that with each rotation of the docking stage, the ESRF device passes through a plurality of discrete rotational positions so as to replicate a circular array of ESRF devices. The processor is configured to calculate an AoA of the incoming signal based on the measured amplitude of the incoming RF signal at each of the plurality of rotational positions. Also disclosed herein is a method for direction finding using a single ESRF device comprising the following steps. One step provides for mounting the ESRF device to a docking stage that is configured to rotate about a z-axis. Another step provides for rotating the docking stage about the z-axis at a rotational speed optimized to facilitate detection of RF signals within a desired frequency bandwidth. Another step provides for monitoring an amplitude of an incoming signal at N rotational positions during each revolution of the docking stage so as to generate at least N samples thereby replicating a circular array of ESRF devices. Another step provides for calculating an AoA of the incoming signal based on the at least N samples. BRIEF DESCRIPTION OF THE DRAWINGS Throughout the several views, like elements are referenced using like references. The elements in the figures are not drawn to scale and some dimensions are exaggerated for clarity. FIG. 1A is a side-view illustration of an embodiment of a direction finding system using a single ESRF device. FIG. 1B is a perspective-view illustration of an embodiment of a direction finding system using a single ESRF device. FIG. 2A is a stop-view illustration of an embodiment of a direction finding system using a single ESRF device. FIGS. 2B, 2C, and 2D are top-view illustrations of an ESRF device at three different time steps. FIG. 3A is a side-view illustration of an embodiment of a direction finding system on a mobile platform. FIG. 3B is a side-view illustration of an embodiment of a direction finding system on a stationary platform. FIG. 4 is a flowchart of a method for direction finding using a single ESRF device. DETAILED DESCRIPTION OF EMBODIMENTS The disclosed methods and systems below may be described generally, as well as in terms of specific examples and/or specific embodiments. For instances where references are made to detailed examples and/or embodiments, it should be appreciated that any of the underlying principles described are not to be limited to a single embodiment, but may be expanded for use with any of the other methods and systems described herein as will be understood by one of ordinary skill in the art unless otherwise stated specifically. References in the present disclosure to “one embodiment,” “an embodiment,” or any variation thereof, means that a particular element, feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment. The appearances of the phrases “in one embodiment,” “in some embodiments,” and “in other embodiments” in various places in the present disclosure are not necessarily all referring to the same embodiment or the same set of embodiments. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” or any variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process,